1. Field of Invention
The present invention relates to a light source device comprising a discharge lamp of the short arc type used as a light source for a projection apparatus wherein light is applied to a light modulation device and an image is produced by the reflected light.
2. Description of Related Art
As known from commonly owned U.S. patent application Ser. No. 11/340,456 published as Publication No. 2006/0170318, a discharge lamp A of the short arc type (hereinafter simply a “lamp”) having xenon gas in an arc tube B, as shown in FIG. 13, is a known light source for projection apparatus, such as projectors. The lamp A, comprising a bulb D having arc tube B, a sealing tube C formed at both ends of the arc tube B, has a anode E and cathode F paired and placed opposite each other inside the arc tube B, Lead pins G support the anode E and the cathode F and are structured so as to protrude outward from the outer edge of sealing tubes C.
Due to the very high pressure resulting inside the arc tube B when lit, to increase radiance, this lamp must be structured so that the sealing tubes C will not break even under high internal pressure, and the lead pins G must protrude from the outer end of the sealing tubes C for electric power to be supplied to the lamp A. Therefore, sealing parts I are formed in the lamp A by using graded glass H on the lead pins G and sealing tubes C.
In recent years, however, due to the trend toward carrying projection apparatus, such as projectors incorporating a lamp such as lamp A, and using them in various locations, there is a demand for smaller projection apparatus, and therefore, smaller lamps. In order to make lamps smaller, the lamp length must be shortened, and in a lamp such as that shown in FIG. 13, the distance L between the back end portion EA of the anode E and the sealing part I must be shortened. However, it has been found that, when shortening this distance L, the sealing part I and the anode E become closer and the temperature of the sealing part I increases due to the high temperature of the anode E when the lamp is lit, thereby causing a problem in which the sealing part I is damaged.
The anode E and the cathode F are placed opposite each other inside the arc tube B, and the lead pins G which support this anode E and cathode F pass through cylindrical retaining bodies J. The portion of the sealing tube C where these cylindrical retaining bodies J are located is heated up, thereby decreasing the diameter to form a pinched part K.
In this pinched part K, the space between the inner face of the openings through which the lead pins G of the cylindrical retaining bodies J pass and the outer face of the lead pins G is not completely welded. The internal space of the arc tube B and the internal space of the sealing tubes C is continuous. A problem occurred in which the gas in the internal space of the arc tube A, which is in a high temperature state, flowed into the sealing tube C, and came into contact with the sealing parts I of the graded glass H, damaging the sealing parts I.
Taking such situations into consideration, to make it possible to cool the discharge gas which flows into the sealing tube C, even if the above-mentioned distance L is shortened in the discharge lamp of the short arc type disclosed in the above noted U.S. Patent Application Publication No. 2006/0170318, a sealing tube cooling component M has been provided on the outside face of the sealing tube C and a lead pin cooling component N has been provided around the circumference of the lead pin G which protruded from the outer edge of the sealing tube C. In so doing, cooling air is blown onto the sealing tube cooling component M and sealing tube C is indirectly cooled through the sealing tube cooling component M, which is cooler than the sealing tube C, thereby decreasing the temperature of the discharge gas which flows inside the sealing tube C. Therefore, it is believed that damage to the sealing part I can be prevented.
However, when the above-mentioned lamp A was actually produced and operated, the temperature of the discharge gas flowing through the inside of the sealing tube C could not be sufficiently decreased for the following reasons, and the sealing part I was occasionally damaged.
As shown in FIG. 14, the sealing tube cooling component M, comprising a plate-shaped body MA having an arc-shaped curved portion MA1 which comes into contact with the sealing tube C and strip-shaped part MA2 which is continuous from the edge of curved part MA1, and another plate-shaped body MB having an arc-shaped curved portion MB1 and plate-shaped part MB2 which is continuous from the edge of curved part MB2, is structured such that the pinnated parts MA2, MB2 overlap. When one strip-shaped body MA is placed in the upstream direction of the airflow, the cooling air only blows directly onto the strip-shaped body placed in the upstream direction of the airflow. The cooling air never directly comes into contact with the other plate-shaped body MB. Therefore, the other plate-shaped body MB is only cooled indirectly by thermal conduction from the plate-shaped body MA through the strip-shaped bodies MA2, MB2 which are mutually adjacent. Therefore, the plate-shaped body MB will be in a higher temperature state than the plate-shaped body MA. As a result, the temperature at the locations in the sealing tube C with which the curved part MB1 of the other plate-shaped body MB comes into contact will not decrease, so it is assumed that the temperature of the discharge gas flowing inside the locations was not sufficiently reduced.
The above-mentioned problem can conceivably be solved by placing both plate-shaped bodies in the upstream direction of the airflow, or more specifically, using a plurality of cooling mechanisms between which both plate-shaped bodies are placed, and having cooling air blow onto both plate-shaped bodies from both directions, thereby cooling both plate-shaped bodies. However, providing a plurality of cooling mechanisms has the disadvantages that the projection apparatus in which the discharge lamp of the short arc type is mounted consequently becomes larger, going against the above-mentioned demand for smaller size, and the noise generated by the projection apparatus becomes excessive, thereby annoying the user.